Internal oxidized Ag alloys are well known. They are useful for various industrial applications, and particularly as electrical contacts.
While they are excellent at refractoriness and antiweldability, their other electrical and physical characteristics such as contact resistance are not entirely even throughout their depth, due to mechanisms inherent to conventional internal oxidation methods.
Conventional internal oxidation methods have solved, to a considerably large extent, to prevent metal oxides from precipitating at a difference of concentration, viz., higher concentration at outer areas and lower concentration at deeper areas. The methods have also prevented metal oxides from very excessively segregating. This is made by the addition to an alloy of an auxiliary solute metal such as In which has a comparatively high diffusion velocity (as described in Shibata U.S. Pat. No. 3,933,485). Or, this is made by the employment of an auxiliary solute metal such as Bi which precipitates at random in an alloy under a normal temperature as noncrystallites which in turn form lattice defects. These lattice defects constitute paths of oxygen and become oxide nuclei to which primary solute metal such as Sn congregates and is oxidized (as described in Shibata U.S. Pat. No. 3,933,486). Though these conventional methods can advantageously be employed for the internal oxidation of Ag alloys, it is often unavoidable, as mentioned above, to see a deplete zone of metal oxides at a deeper area of alloys.
On the other hand, although those electrical contact materials which are made by powder-metallurgically sintering or hot pressing metal oxide powders with Ag powders, are uniform in their distribution of oxides, they are inherently coarse and brittle.